Automatic Print Quality Inspection Technology

Today, in the printing and packaging industry, more and more manufacturers have the financial ability to purchase various types of advanced printing and post-press processing equipment. With the improvement of printing equipment, various high-grade prints are also increasing. While looking at domestic printing companies, some of them already have advanced and similar equipment and have the same production technology capabilities, but the result is similar products and companies lack competitiveness.

The key to how a printing company can maintain its leading position in the industry and obtain a reasonable profit is whether the company itself can provide non-homogeneous characteristics. For example: unique new technology and good, stable print quality. However, the unique new technology and good and stable quality are difficult to measure with money. Moreover, in terms of quality, the company must have a reasonable and complete quality management system in order to have a good and sustained overall quality for a long time.

Whether it is a manufacturer or an end user, everyone wants a good, stable quality. In theory, the quality of a good print should be an agreement negotiated and confirmed by a manufacturer and end-user for a particular print, and must be clearly and quantifiable and reasonably described. Although there is a certain standard in the definition of "quality" of the domestic brush product at present, because of the different printing standards and the different standards, it is more likely that the inspection results will be affected when the printed matter is actually inspected. Excessive external factors and human factors make it difficult to achieve uniform and quantifiable stability standards. How can we achieve a uniform, quantifiable and stable quality standard? Industry insiders are eager to establish such a quality standard as soon as possible and are actively seeking a reasonable and best way to test it.

In terms of printing quality inspection, countries such as Europe, America and Japan have made great progress. As early as the 1970s, there have been vendors actively working with image processing systems to digitize visual information, achieve "seeing" and "cognition" of print quality through computers, and conduct high-speed, high-precision printing on printed materials. 100% real-time detection completely eliminates human errors and establishes a uniform and quantifiable inspection standard. At present, BOBST in Switzerland, PROIMAGE in the United States, DAC in Japan, and TOKIMEC can provide full automatic print quality inspection equipment.

Automatic Print Quality Inspection Equipment

1. How it works

The detection system used in automatic print quality inspection equipment is to first take a standard image using a high-definition, high-speed camera lens, set a certain standard on this basis, and then shoot the detected image, and then compare the two. The CCD linear sensor converts the change in the light quantity of each pixel into an electronic signal. After the comparison, if the detected image is different from the standard image, the system considers the detected image to be a defective product. The various errors generated in the printing process are only different from the standard image and the detected image for the computer, such as defects such as smudges, ink spots, and the like.

2. Detection accuracy

The earliest used for print quality inspection is the technology of comparing the gray scale of the standard image with the detected image. Now the more advanced technology is based on the RGB three primary colors for comparison. Where is the difference between fully automatic machine detection and human eye detection? Taking human eyes as an example, when we look at a certain printed matter intently, if the contrasting color of the printed matter is relatively strong, the smallest flaw that the human eye can find is a defect with a contrasting color that is not less than 0.3 mm; but it depends on people. It is difficult to maintain consistent, stable visual effects. In another case, if defects are found in prints of the same color, especially in a light color system, the defects that the human eye can detect need at least 20 gray levels. An automated machine can easily detect a 0.10mm defect, even if the defect is only one grayscale difference from the standard image.

However, in terms of practical use, even the same panchromatic contrast system has different ability to discriminate color differences. Some systems can find contours and defects with large variations in color, while others can identify very small defects. For white cardboard and some simple style prints, such as the Japanese KENT cigarette label, the United States Marlboro cigarette label, simple detection may be sufficient, and most of the domestic print, especially various labels, has many characteristics, With too many flash elements, such as gold, silver cardboard, hot stamping, embossing, or polishing prints, this requires that the quality inspection equipment must have sufficient ability to find the smallest grayscale differences, perhaps 5 shades of gray. The difference in level may be a stricter one gray level difference. This point is crucial to the domestic label market.

The accuracy of the comparison between the standard image and the printed matter being examined is a key issue in the detection equipment. Usually, the detection equipment collects the image through the lens. In the middle part of the scope, the image is very clear, but the image at the edge may be false. Shadow, and the detection result of the phantom part directly affects the accuracy of the entire test. From this point of view, if only the comparison of the full width area is not suitable for some fine prints. If the obtained image can be subdivided again, for example, the image is divided into 1024dpi×4096dpi or 2048dpi×4096dpi, the detection accuracy will be greatly improved, and at the same time, because the phantom of the edge portion is avoided, the detection result is more stable.

3. Detection parameters

After setting the quality inspection parameters, will the use of high-speed, automated quality inspection equipment lead to excessive scrap rates? The increase in scrap rates will undoubtedly lead to lower profits. But in fact all quality standards are relative, such as the generally unacceptable minor defects, if it is in certain areas (gluing, subsistence) is acceptable. In the case of manual detection, an appropriately relaxed, flexible standard can be automatically formed. How can rational and data-based detection be completed? It is more reasonable for the printer and the end-user to reach an agreement to adopt a sub-regional and hierarchical quality inspection standard for the printed matter. This is only a rigid rule, but must be a quantifiable standard that can be manipulated and accepted by all parties. And these standards must be all kinds of data set by the user, such as the area to be detected, the detection level of each area, and the testing standards to be performed at each detection level.

First, we partition the detected prints, as shown in Figure 2. In the figure, A is the most rigorous testing area - the most important part of the printed matter (trademarks, products); B is the rigorous testing area - important part (product); C is the general testing area - background; D is the neglected area - concealed Part (glue wing, life part)

Then, set each detection level. This point is very critical, it will directly relate to the ability to find defects, but also directly related to the number of reject rates, so customers will certainly require an acceptable and reasonable range of tolerances, including the setting of acceptable, defect-size Range tolerance, acceptable, defect gray tolerances.

Application of Print Quality Inspection Technology

1. Application of automatic print quality inspection technology

From the equipment point of view, fully automatic print quality testing equipment must be able to adapt to different production processes, in particular, must adapt to the complexity and diversity of the domestic printing process, therefore, must have different equipment to meet the testing requirements of different customers. If the printing process is divided, there will inevitably be user-selectable connection detection devices and off-line detection devices. The more ideal situation is to subdivide offline detection devices into single-sheet detection devices or cassette detection devices. For connection detection equipment, it should be able to find problems in the production process in a timely manner, alert operators to take measures to solve problems, reduce waste products, and increase profits for enterprises; for off-line inspection equipment, it is an after-the-scenes screening of print products and analysis of production processes. Help the management of the company get more information and assist the internal management of the company. Relying on the capabilities of equipment suppliers, end-users can choose to test equipment offline, and printing manufacturers can freely combine in multiple options to achieve 100% inspection.

Take Japan's packaging and printing manufacturers as an example, the economical and reasonable quality control method is to first select the connection test equipment and remove the defective printed matter; secondly, cooperate with other off-line testing equipment to do targeted detection on the printed products that have been removed. Wired detection is used for process control, finding problems, reducing problems, and minimizing the possibility of recurrence of the same problem. The off-line testing equipment that cooperates with it is to further improve the quality system and achieve 100% inspection.

Another option is to first rely on the speed of a sheet-fed inspection device to pick out defective single-sheet prints from the entire printed matter. These prints should also have good prints intermixed, and the detection equipment can be used to pick out those good ones. The prints.

In order to meet the more complex requirements of customers, testing equipment must have enough flexibility. If only the work of “inspection” (discovery of defects) is performed and there is no function of “separation” (differentiating between qualified products and defective products), then the meaning of “inspection” will be greatly reduced, and therefore it is required that the testing equipment must perform “inspection” at the same time. "and" points "function. Of course, there are more and more practical considerations, such as whether the connection test equipment can be installed more flexibly and more mobilely. Can you have more choices according to the customer's actual situation? Some customers will require double-sided inspection, and some customers will require the camera's detection accuracy to be increased to 0.05mm, and customers will require only the detection of specific colors.

2. Increased management efficiency

Although some printing companies in China have begun to pay attention to automatic print quality inspection equipment, some people think that the detection of automatic detection equipment does not differ significantly from manual detection. Actually, human detection, although the test results are acceptable, lacks specific data and cannot even tell which process was the waste product. This test result is quite unfavorable for the management of a company. The use of testing equipment for quality testing provides real-time reporting of the entire process and detailed and complete analysis reports. The on-site operator can rely on the timely detection of the automatic detection equipment and timely adjust the problems in the work according to the real-time analysis report. It is possible that the reduction will be not only a percentage point scrap rate, the manager can analyze the report based on the test results. Tracking the production process is more conducive to the management of production technology. Because of the high-quality testing equipment required by customers, not only does it stop at the quality of the printed matter, but it also requires the ability to analyze afterwards. Some quality inspection equipment can not only improve the qualification rate of finished products, but also help manufacturers to improve the process and establish a quality management system to achieve a long-term stable quality standards.

3. Increased market demand

What are the reasons for the Japanese companies to first adopt the automatic print quality inspection equipment? In Japan, the food packaging and pharmaceuticals, cosmetics packaging industry, industry associations strictly regulate the quality standards of packaging and printing plants, in addition to direct containers, more strictly The related product names, methods of use, and in particular the printing quality of the labels on the inner and outer packagings are specified. Because there have been accidents caused by accidental taking of drugs due to the printing of drugs on the outer packaging of medicines, the number of dots has been printed. Visible, the importance of label printing quality, in addition, in the food packaging industry, in addition to strict management in the production process, but also all the packaging to be tested to prevent small omissions so that companies lose a good reputation. Of course, one of the reasons is to reduce the large amount of expenses required for manual testing.

More importantly, people pay more and more attention to the modern business economy.